A high temperature fatigue (HTF) life prediction model is developed based on the concept of microcrack propagation. The model is used to correlate isothermal HTF and thermomechanical fatigue (TMF) life for the Ni-base superalloy MAR-M247. The mechanical strain versus temperature relationships for the TMF tests include in-phase, out-of-phase, and a counter-clockwise diamond history. The proposed model explicitly accounts for damage from all three HTF damage mechanisms: fatigue, oxidation, and creep. The fatigue and oxidation components are correlated using the ΔJ parameter with an additional time dependence included in the oxidation term. The creep component is correlated using a stress power release rate-type parameter, Cˆ. In this paper, we focus on application of a model to HTF and TMF of Ni-base superalloys. However, the basic model features may well apply to other classes of metallic materials.

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